All you need is 2 people at least 500 or so miles apart to measure the shadow of the sun at the same time on the same day. Simple geometry will prove that the earth is round, cause if it was flat, the angle any object would cast a shadow would be the same no matter where you are located.
Or the fact that if you go far enough north or south, the sun will never appear directly overhead at any day of the year.
I travel on both sides of the equator and can tell you where the sun is in the sky between Stavanger, Luanda and Cape town. Also the moon and the constalations are upside down for my reference as someone who grew up in the north. Not to mention you can't see the southern cross from the US or Polaris from Mauritius.
Now here come the flat fucks who have never left the city they were born in with "facts" and thousands of troll video's from fucktards trying to get hits for their bullshit page.
Carry on
Shit made no sense.
And I'd love to see the equation of your simple geometry.